Company not giving experience letter till I pay them. I've doubts in amount. They reply after weeks.

My company firstly extended my Probation without giving any reason. When extended probation was ending, they didn't confirm me. They terminated me saying performance issue. I didn't agree to this reason. But manager didn't hear me. I did not even get to talk to HR. I refused to sign the Termination Letter also. One day after I left the company, they paid me 3 months Basic Salary without any deduction. After 9 days, they mailed me saying that they overpaid me, and I have to return then 1.72 lakhs. 1 lakh was joining bonus and remaining 72 thousand was a Tax component. I immediately raised concern that I am not eligible to refund the joining bonus, because it is the company who terminated me. Now, company's response is veryyyyy slow. First they denied. They said that I have to return Joining Bonus. I mailed them again with screenshots of policy. They forwarded my mail to my manager. He took 23 days to reply back. But finally. they agreed that I don't have to refund 1 lakh. They said that they'll send a new slip after 16 days, on 29th March. I waited. On 29th's slip, they again made a mistake. I again mailed them. Its more than 2 weeks, they haven't reverted. I am sending daily follow up mails since a week now. But they never reply anything. Its been 2.5 months already and they haven't given me Experience Letter and Relieving Letter. Recently, I cracked interviews in 2 other companies. But both asked for Experience Letter. Even the company's Separation site says this - "If you don't make the payment or if you delay the payment, the relieving and experience letters will not be issued. Any background verification requests received will be rejected." My concern is - Firstly, the company terminated me. Then they paid me extra. Then they demand refund. When I raise question, then answer very very very slow. And I am suffering because of their termination, miscalculations, delays and policies. What should I do?